Field of the Invention
The present invention relates to an electronic apparatus, a system for estimating degradation of an internal power supply, and a method of estimating degradation of an internal power supply. More particularly, the present invention relates to an electronic apparatus capable of estimating a degree of degradation of the electronic apparatus, a system for estimating degradation of an internal power supply, and a method of estimating degradation of an internal power supply.
Description of the Related Art
Many electronic apparatuses include an internal power supply formed with a capacitor, a battery, a secondary battery, an electricity storage device, or the like. When electrical power of a correct value is not output from such an internal power supply due to severe degradation of the internal power supply, the electronic apparatus functions in a wrong manner, or fails to function at all. Therefore, various techniques have been developed for determining degradation of an internal power supply.
There are various kinds of methods known as methods of determining degradation of an internal power supply. For example, degradation of an internal power supply can be determined from a phenomenon in which the voltage of the internal power supply (or the voltage between the positive terminal and the negative terminal of the internal power supply) drops due to the influence of the internal resistance or the like of the internal power supply when the supply of power to the internal power supply is stopped, as disclosed in JP 2000-299137 A and by Masaki MURAYAMA, et al. in “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery”, Mie Prefecture Industrial Research Institute Report No. 34 (2010), Mie Prefecture Industrial Research Institute (searched online, Nov. 5, 2014) (URL:http://www.mpstpc.pref.mie.lg.jp/KOU/kenhou/h21.htm).
As disclosed in JP 2000-299137 A and “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery”, and as schematically shown in FIG. 13, when the current supply to an internal power supply is stopped, the voltage V rapidly drops (see ΔV1 in FIG. 13) immediately after the stop of the current supply, and after that, slowly drops with time (see ΔV2 in FIG. 13, this component is also called the “relaxation” component in “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery”).
For example, JP 2000-299137 A discloses a secondary battery state determination method for determining the degree or the state of degradation of an internal power supply from the voltage drop ΔV1, an internal resistance R1, and the like on the basis of the finding that, in a case where the internal power supply is degraded, the rapid voltage drop ΔV1 immediately after the supply of power is stopped (or the internal resistance of the internal power supply calculated according to R1=ΔV1/I0, which uses the current value I0 at the time when the supply of power is stopped) is larger than that in a case where the internal power supply is not degraded.
Meanwhile, “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery” discloses that the internal resistance of an internal power supply calculated based on the above described rapid voltage drop ΔV1 is higher in a case where the internal power supply is being used than that in a case where the internal power supply is in a brand-new state, and, after degradation of the internal power supply, the internal resistance is lower than that in the case where the internal power supply is being used. As for the “relaxation” resistance component calculated from the voltage drop ΔV2 at the time when the voltage V slowly drops after the rapid drop, the “relaxation” resistance increases monotonically as the internal power supply is degraded from a brand-new state to a used state to a degraded state, as disclosed in “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery”.
In view of this, the inventors made a study on a method of determining a degree of degradation of an internal power supply based on the above mentioned “relaxation” component or the voltage drop ΔV2 in a state where the voltage V of the internal power supply slowly drops with time (this state will be hereinafter referred to as a relaxed state as in “Study on Voltage Drop during Charge-discharge Test of Li Ion Secondary Battery”) after the rapid drop of the voltage V immediately after the supply of power to the internal power supply is stopped.
As a result, the inventors have obtained the finding that a degree of degradation of an internal power supply can be appropriately estimated in some cases, but cannot be appropriately estimated in other cases. Based on this finding, a degree of degradation of an internal power supply is estimated in a situation where a degree of degradation of an internal power supply can be appropriately estimated. In this manner, the degree of degradation of an internal power supply is accurately estimated, and a severely-degraded internal power supply is replaced with a new one. Accordingly, an internal power supply can be prevented from failing to output electrical power of a correct value. Thus, an electronic apparatus can be appropriately prevented from functioning in a wrong manner or failing to function.